Natural History and Larval Behavior of the parasitoid Zatypota petronae (Hymenoptera: Ichneumonidae)

Abstract

The koinobiont ectoparasitoid Zatypota petronae Gauld (Ichneumonidae) parasitizes medium-sized immatures of the cobweb spider Theridion evexum Keyserling (Theridiidae). Zatypota petronae apparently attacks the spider inside its retreat. An egg is glued on the antero-lateral dorsal section of the spider’s abdomen. First-instar larvae remain partially inside the egg chorion which is attached to the spider’s abdomen. In later instars, a layer of a brownish material (saddle), to which the 7th and 8th abdominal segments of the larva adhere ventrally, anchors the larva to the spider. In the last instar the saddle includes the egg chorion and the shed exoskeletons of previous instars. A row of retractile, dorsal protuberances, crowned with hooklets, is present on abdominal segments 1 to 8 of the final-instar larva. The larva uses the hooklets to grab silk lines of the retreat of the spider’s web. Hanging on the spider’s web the larva kills the spider and sucks out its body tissues. Then the larva pushes vigorously laterally with its head against the spider’s corpse, and alternately presses the corpse against the saddle. These movements, in combination with peristaltic movements, free the larva from the saddle that falls to the ground with the dead spider. The larva then constructs its pupal cocoon. Prior to cocoon construction, the larva induces the spider to reinforce the retreat by adding more threads. Parasitism rate and host behavior are also described.